248 THE POPULAR SCIENCE MONTHLY. 



stream has along its sides its complement of nerves nearly parallel. 

 Between these nerve-fibers lies the undifferentiated protoplasm, or life- 

 stuff, which is the supply of constructive matter for the use of these 

 tinv builders, for out of this life-matter, or bioplasm, each cell is 

 built. But even mortar may need quickening so this life-stuff may 

 become too passive, that is, quasi torpid. These nervous fibrillae are 

 the electric wires, and gentle friction is the dynamo to generate the 

 mysterious fluid and quicken the conductivity along the lines. 



Strange to say, this scratching has also its psychological side. Let 

 a puzzle be propounded, and why on the instant does the nonplused 

 one institute a rummaging for an idea in the hirsute thatch of his 

 cranium ? And everybody does it, even he " of the front of Jove 

 himself " more than the beetle-headed clown. We asked an explana- 

 tion of our encyclopedic friend who " knows it all," and quoted to him 

 the well-worn distich : 



" Be mindful, when invention fails, 

 To scratch your head and bite your nails." 



Upon the word he began disheveling his carefully brushed hair, say- 

 ing it was " a poser," and, by way of compliment, that it " was not 

 slow " ; to which our response, " No, it's Swift " ; at which he laughed, 

 though he had quite missed the point, for he rejoined that he always 

 thought us " a little fast." 



It is truly wonderful how lavishly and admirably Nature has gifted 

 many animals for this very exercise of scratching lightly with the claws. 

 At my feet lie Tom and Dick, two good friends. The former is a fine 

 young Maltese, the latter an old black-and-tan. The cat's claws are 

 very sharp, the dog's are less so. Both animals are clean and in good 

 condition, yet both appear to take delight in a good scratching at the 

 back of the head, and especially behind the ears. The hind-foot is the 

 instrument used, and with what delicacy yes, nicety, or precision of 

 adjustment ! So rapidly does that foot move, that it makes a fan-like 

 shadow ; and so exact the distance at which the keen, protruded claws 

 are set, that it secures only a delicate touching of the parts, producing 

 the pleasant titillation of the tonsorial brush. Any coarser adjustment 

 of those needle-pointed hooks and the blood would flow from the lacer- 

 ated skin. 



But, even more than with the mammals, is this cuticular titillation 

 a necessity with the ordinary fishes ; and, since they have neither 

 hands nor feet, how is this want in their case gratified ? I have wit- 

 nessed the operation many times, yet fear a failure to adequately de- 

 scribe it. The scaly coating of a fish needs an occasional cleaning, as 

 does the copper sheathing of a ship ; for, with both, a foul surface im- 

 pedes progress through the water. On each side of a typical fish is a 

 thin line, known as the lateral line. It is, in fact, a mucous canal, from 

 which issues at the will of the animal a lubricating fluid, which, spread 

 over its scaly sheathing, lessens friction, and so facilitates movement 



